Because Facebook started this behavior, so many social software started this approach, of course, there is a saying that Facebook also wants to introduce their cryptocurrency, so they banned other cryptocurrencies.

If we look at this objectively then can we really blame them? Go look at twitter with all the "Send me 1 ETH and I send you back 10 ETH" scams.
A lot of people are getting scammed, mostly new people who don't understand the first thing about the technology.

I think some GOOD regulation and prosecution of these scammers will clear the air and let the ads become legal again. But for now I personally do not hold it against google and facebook. It is understandable that they take legal risk for things like having bitconnect ads and so on.

Governments for the most part seem to welcome cryptocurrency, I think once they clear the air then we are good to go and can move forward. Good projects will suffer unfortunately without access to advertising, but itl turn out better for us in the long run.
Cryptojacking probably also plays a large role in this.

Allow them to do so, twitter is a drop in the ocean compared to facebook and google. It will make little to no difference and I'm also fairly sure the decision will be reversed in a few years time once the ICO space is much better regulated.

Social media ban on cryptocurrencies ads

This is what I always say, this whole crypto thing is so new that people needs to have at least a minimum education to be able to deal with it safely... (if they care about safety... electricity is much more older than the cryptos but people are still drying their hair in the bath tube still.... well...)
The sad thing is that in the western countries, people are still not have the necessary education to deal with their fiat money (pyramid schemes, etc...) so it will not be easy to educate them about cryptos...